Pennsporter says the building is about 3,000 square feet, going all the way back to adjacent Hancock Street:

It could certainly house a good sized gym in the Cross Fit mold, similar to that of Fearless Athletics near Hawthorne’s at 11th and Fitzwater Street. As you know, this area of the neighborhood has taken off recently – the presence of Federal Donuts, Herron Playground, and new housing make this the epicenter of the new Pennsport development.